| Author | Message | ||
| Rijk Rietveld (Rijk365gtb4)
Junior Member Username: Rijk365gtb4 Post Number: 122 Registered: 1-2002 |
I hear a real Lotus-man | ||
| Ken (Allyn)
Member Username: Allyn Post Number: 680 Registered: 10-2001 |
Dynos are one thing, but what about air resistance in real world driving? A slipperier shape is more speed per HP. Also, cornering ability is a component of much more than HP. HP is important but many cars with lower HP are faster both on the road and track. | ||
| Mitchell L. Davidson (Jussumfastgi)
Member Username: Jussumfastgi Post Number: 388 Registered: 4-2002 |
Rob, you are correct. The latest cobra is under rated by almost 50hp, the Viper GenII was under rated by a little over 20hp, and the Camaro Z28 SS was underrated by 15hp. When will Americans learn to build a car?  Come now, there is no need to throw stones. No car on earth was overrated more than the Countach QV. | ||
| Tim N (Timn88)
Intermediate Member Username: Timn88 Post Number: 2106 Registered: 6-2001 |
The mustangs were bad because of a piece of metal in the intake manifold left from the casting process that was blocking air. 3% accuracy sounds right. Thats actually very close. Dynos have temp and humidity sensors and usually automatically correct the numbers. My friend dynoed his 99 camaro and it pulled 302rwhp 317rwtq. the dyno was reading 10hp low for everone because the temp sensor was next to a cold wall, so the cmputer thought the car was getting colder air then it acutally was. This camaro is an automatic, so thats 18%-20% loss. It barely has any mods, just an exhuast, intake lid and a few home made things. assuming 18% loss with the 10hp lower 302rwhp, it has 356 crank hp. not bad for a car rated at 320. It is known that GM under rated these cars by up to 20hp. they had alot more than 320 stock. | ||
| Rob Lay (Rob328gts)
Board Administrator Username: Rob328gts Post Number: 3355 Registered: 12-2000 |
http://www.ferrarichat.com/discus/events/dyno2002/ I think about all the cars came out about right. All were stock that I knew of, even mine before the K&N was showing stock numbers. I would bet most Ferraris to come within 10 HP of rated. I heard American cars are really bad about this. When the last generation Mustang Cobra came out there was a huge discrepancy of 30-50 HP. | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 312 Registered: 4-2002 |
Many things come into play, here: Distribution of engine output (actual) probably around 3%. Heck, even the most carefully machined and assembled engines in the world (F1) have variances that make one motor the race motor (spot on), another a qualifying motor (+20HP), still another nothing more than a test mule (-10HP). Then there is the difference between American HP (SAE) and german (DIN) and japaneese (???) at the definition level itself! An HP quote from one system is inaccurate in another. Then there is the accuracy of a dyno. If you took the same car, running the same gasoline, oil, at the same operating temperature,... to a dyno 30 days in a row, I would expect to see a nice Gaussian distribution of 3% over those runs AFTER correcting for standard temp, pressure and humidity. Back to back runs often show almost 2% differences. Given all this: any number within 5% (of any ture reference standard) is accurate enough. | ||
| Rob Schermerhorn (Rexrcr)
Junior Member Username: Rexrcr Post Number: 158 Registered: 11-2002 |
William, I congratulate you on dynoing your car. Speculating how much power you car produces proves what? Let's get the numbers and see for ourselves. I'm working with Michigan region FCA to organize a dyno day just for this reason. Fun stuff. Ps, sound like you put your car on an inertia dyno, like a Dynojet. A shock dyno measures shock absorber (damper) data such as force vs. velocity. One removes the shock absorber from the car and installs it on a machine that cycles the shock to simulate use on a car. And 15% estimated drive train loss works out to 453 hp at the flywheel. (385/ 0.85) I have dyno'd Ferraris, the numbers work out very close to what the factory claims. And the factory numbers must conform to internationally agreed testing standards, so the days of "gross" hp numbers are gone. This takes parasitic losses into account, more "real world". Dyno a F355 engine on an engine dynamometer and it should read about just over 400 hp at the flywheel. | ||
| William H (Countachxx)
Intermediate Member Username: Countachxx Post Number: 1804 Registered: 2-2001 |
I had my 512TR on a shock dyno where you place the rear tires on the dyno & it measures rear wheel hp. She was making 385 that day. Taking into account a 15% driveline loss the engine was making close to 460 hp. factory rating is 428 hp | ||
| Mike B (Srt_mike)
New member Username: Srt_mike Post Number: 34 Registered: 12-2002 |
Michael, PSK hit the nail on the head. There are manufacturing variations that can account for a large range of horsepower outputs. 10% would not be uncommon between the 5th and 90th percentile. So, when they say your car makes 421 - does it really? Or does it actually make somewhere between 390 and 430? And if it really makes somewhere in that range, won't the guy who gets 390hp be peeved that he got "less than he paid for"??. Since you're already adjusting the numbers to meet a percentile rating, why adjust them to the nearest single digit and not 5 or 10??? I'm wondering what the answer to that is. Is it because they don't under-rate them and they pick the strongest one and rate it at that? | ||
| PSk (Psk)
Junior Member Username: Psk Post Number: 64 Registered: 11-2002 |
Accuracy is almost irrelevant here, though because of manufacturing tolerances (yes, even Ferraris) NOT all engines will produce the same power. Thus I agree with Mike, should just round down to the nearest 5 hp ... but I do not think Italians round down, they pick the best engine, and remove power sapping real world stuff and go for broke, and thus with a big bragging smile, tell everybody that the engine produced X hp before it spat a rod across the room But heh, it does sound contrived saying 450hp, where 453 sounds real. In the end when I read manufactures quoted hp figures, I always factor in the manufacturer, ie: Porsche/Merc: Probably accurate, infact a Porsche off the lot could even be better. Lambo: Total Italian exaggeration, lucky to be within 50 hp. Ferrari: Again Italian exaggeration, but less to prove, thus lucky to within 20 hp. Alfa Romeo: Hmmm, again probably exaggerated, +20hp. In the end only way to prove is to stick your car on a calibrated dyno, with an expert operator ... and find out ... even then there are many variables (humidity, etc.) ... but many race series equalise cars before the series by running on a master dyno. My 1 cent post. Pete | ||
| Michael N. (Man90tr)
Member Username: Man90tr Post Number: 755 Registered: 4-2001 |
Why is accuracy weird? Assuming this is the reason for the number. If the company knows accurately that the engine is producing 421 Hp, why tell me 420? If its 398, why tell me 400? And so on? i think its odd to give me a fake number. | ||
| Randall Booth (Randall)
New member Username: Randall Post Number: 31 Registered: 1-2003 |
Sorta on this topic.... Does anyone know the power restored when the smog equipment is taken off a 308? This includes the cats. | ||
| Mike B (Srt_mike)
New member Username: Srt_mike Post Number: 33 Registered: 12-2002 |
Still looking for a pristine yellow 512M (tall order - any out there?). I find it strange that Ferrari rates their cars at odd numbers. Any idea why this is? I don't see much dyno data on stock cars, so it's hard to know where they fall in relation to the factory. Usually, a manufacturer rates a car such that some large percentage (probably 95%+) make the advertised power. If you're "rounding down" you would most likely pick a multiple of 10 or maybe 5. Most cars are rated 450, 505, 350, 300, etc. But many Ferraris are rated at, say 392, 438, etc, etc. Anyone know how Ferrari comes up with their power ratings? The other place I have frequently seen this is in tuner cars (i.e. AMG). I always figured they did this so they could quote a higher number than the factory bell-curve-safe number. How does Ferrari arrive at their quoted HP numbers? Has anyone dynoed a stock car? How did it compare to the factory rating? |